The dynamics of sponge larvae assemblages from northwestern Mediterranean nearshore bottoms

Abstract

In this study, we show for the first time the dynamics of sponge larvae assemblages from nearshore meroplankton. Plankton was collected by SCUBA diving once or twice a week during a 2-year period over a rocky artificial reef in the NW Mediterranean. Data on larval abundance were cross correlated with the values of environmental parameters (i.e. seawater temperature, solar radiation, wind speed and atmospheric pressure). In the laboratory, we recorded external features and main behaviors of larvae. We collected larvae belonging to 20 different taxa of sponges, which are among the most common in the sublittoral hard bottom communities of the NW Mediterranean and other temperate areas. There was a positive correlation between maximum abundance of larvae and highest water temperatures. Maximum solar radiation preceded the maximum of larval abundance. Wind speed showed no clear seasonal patterns and atmospheric pressure was overall the lowest when larvae were most abundant. Two main patterns in the larval release periods were observed. One was shown by species releasing larvae in summer, right before the maximum water temperatures (orders Dictyoceratida and Dendroceratida) and another by the species whose larvae release from the end of summer till autumn, when temperatures decrease (order Poecilosclerida). The larvae of Phorbas tenacior, Raphidoflus jolicoueri, Mycale rotalis, Tedania anhelans, Pleraplysilla spinifera, Aplysilla sulfurea var. rosea and Chelonaplysilla noevus are described for the first time. The larvae collected mainly belonged to the parenchymella type (except for the species Oscarella sp. and probably Cliona viridis) and showed different features and behaviors: from the elongated parenchymellae of Scopalina lophyropoda (order Halichondrida), which show simple swimming behavior and no response to light, to the parenchymellae of Poecilosclerida and Dictyoceratida orders with variable morphologies as adaptations to complex swimming behaviors. Our database will hopefully contribute to the present knowledge of larval types in sponges and definitively highlight the importance of this group in the dynamics of meroplankton from nearshore bottoms. © Oxford University Press 2005; all rights reserved.